Lipid a modifications characteristic of Salmonella typhimurium are inducedby NH4VO3 in Escherichia coli K12 - Detection of 4-amino-4-deoxy-L-arabinose, phosphoethanolamine and palmitate

Two-thirds of the lipid A in wild-type Escherichia coil K12 is a hexa-acyla ted disaccharide of glucosamine in which monophosphate groups are attached at positions 1 and 4', The remaining lipid A contains a monophosphate subst ituent at position 4' and a pyrophosphate moiety at position 1, The biosynt hesis of the l-pyrophosphate unit is unknown, Its presence is associated wi th lipid A translocation to the outer membrane (Zhou, Z,,White, K, A, Polis si, A., Georgopoulos, C,, and Raetz, C. R, H, (1998) J, Biol. Chem. 273, 12 466-12475), To determine if a phosphatase regulates the amount of the lipid A 1-pyrophosphate, we grew cells in broth containing nonspecific phosphata se inhibitors. Na2WO4 and sodium fluoride increased the relative amount of the 1-pyrophosphate slightly. Remarkably, NH4VO3-treated cells generated al most no 1-pyrophosphate, but made six major new lipid A derivatives (EV1 to EV6). Matrix-assisted laser desorption ionization/time of flight mass spec trometry of purified EV1 to EV6 indicated that these compounds were lipid A species substituted singly or in combination with palmitoyl, phosphoethano lamine, and/or aminodeoxypentose residues. The aminodeoxypentose residue wa s released by incubation in chloroform/methanol (4:1, v/v) at 25 degrees C, and was characterized by H-1 NMR spectroscopy. The chemical shifts and vic inal coupling constants of the two anomers of the aminodeoxypentose release d from EV3 closely resembled those of synthetic 4-amino-4-deoxy-L-arabinose . NH4VO3-induced lipid A modification did not require the PhoP/PhoQ two-com ponent regulatory system, and also occurred in E. coli msbB or htrB mutants , The lipid A variants that accumulate in NH4VO3 treated E. coil K12 are th e same as many of those normally found in untreated Salmonella typhimurium and Salmonella minnesota, demonstrating that E, coil K12 has latent enzyme systems for synthesizing these important derivatives.